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Nature Armadillos

Nature's True Survivors: 'Dillos

ArmadilloThe sound of leaves rustling in winter wouldn't excite everyone. But Dr. Lynn Robbins, a Southwest Missouri State University biology professor, isn't everyone. When Robbins heard crunching leaves recently in Taney County at the university field station, he ran to investigate. He found a scrawny armadillo sniffing about in the leaves. It was using its narrow snout to search for food. This was very exciting, he said, because the animal should not have been here at all. 

Robbins was surprised to find the animal because research shows armadillos should not have survived the severe conditions of this past winter. In fact, the winter's snow had melted only a week before he spotted it at the field station. Before the day was over, Robbins said he spotted three other skinny armadillos while working at the Field Station. All were slow to react to him, which he attributed to the animals' lack of energy from the cold and lack of food.

Armadillos are found all over the southeast and south central United States, and have traveled as far north as Missouri.  They first arrived in Missouri in the early 1980s.  By last summer, many had made their homes in Southern Missouri. Biologists thought that the harsh winter might have killed many of them. 

Armadillos cannot tolerate cold climates and so cannot live too far north. The dry climate of the west is also unfriendly because the soil is not moist for digging and burrowing, which is how they find their favorite foods.

Compared to other mammals, armadillos have relatively low body fat, which makes it hard for them to maintain their body temperature. To burn calories and stay warm, they need to eat a lot of insects, larvae, ants and beetles, and sometimes a snake or lizard. Winter temperatures, ice and snow prevent the armadillo from foraging for these foods. Their acute sense of smell and their long claws are useless for digging in frozen or snow-covered ground. 

Another way they keep warm is by using the veins and arteries in the legs to circulate heat as well as blood.  Hot blood leaving the body and going into the legs, is cooled by cold blood coming back into the body and vice versa. The process is called reta mirabila. Cold weather can make frostbite more likely for these already cold feet. 

Robbins is conducting a statewide survey to determine whether the cold, icy winter slowed the spread and the numbers of armadillos in Missouri. He is sending surveys to biologists, conservationists, land specialists and state agency officials asking them to record armadillo sightings. The same survey will be distributed again in fall 2001, and final results will be available in summer 2002.

Even if they report seeing a large number of armadillos, Robbins says it won't prove that the winter had little effect on the 'dillos.  Armadillos that survive will be hungry and will come out to hunt more frequently, which makes them more likely to be seen, he explained.  And, he said, people may report seeing several armadillos although they actually see the same animal more than once.

Although research suggests armadillos are unlikely to have lived through the winter, Robbins believes that the population will recover because of the ways armadillos reproduce.

A female armadillo gives birth to four identical young, which come from the same fertilized egg.  After her egg is fertilized, she may wait before letting it grow if environmental conditions are stressful.  Surviving female armadillos this year are likely to be weak and may wait to begin pregnancy. This would give future generations a better chance to survive.

Source: Adapted from an article by Jen Zarcher of Bull Shoals Field Station. Photo: US Fish & Wildlife Service.
Bull Shoals Field Station is a center for research and education focused on the outdoor world.  The Field Station, operated by SMSU, is located on the western end of Bull Shoals Lake and next to the 6,000-acre Drury-Mincy Conservation Area. SMSU faculty, graduate students and visiting scientists do research here at all seasons of the year.
The armadillo survey is available at http://armadillo.smsu.edu
To learn more about SMSU's Bull Shoals Field Station, visit the web site at http://www.bullshoals.smsu.edu